Distance is a fundamental concept in kinematics, often confused with displacement, but it serves a very distinct purpose. It measures how much ground an object has covered during its motion, regardless of which way it travels. Think of it as a complete record of your journey without paying attention to where you started or where you ended up.
For example, if you drive your car around a block and return to your starting point, your displacement might be zero, but your distance is the total length of the path you traveled around the block.
- Distance is always a positive quantity because you only sum the path taken.
- It includes every forward and backward move without considering the move's direction.
Understanding this, let's look at a train journey on a straight track. If the train travels 5.9 km forward and then reverses 3.8 km, the distance it covered is the total path it journeyed, calculated by adding the forward and backward distances: \[5.9 \, \text{km} + 3.8 \, \text{km} = 9.7 \, \text{km}.\] Therefore, the train covered a distance of 9.7 km.